Low temperature charging of Li-ion cells

Abstract

A battery cell charging system, including a charger and a controller, for low-temperature (below about zero degrees Celsius) charging a lithium ion battery cell, the battery cell charging system includes: a circuit for charging the battery cell using an adjustable voltage charging-profile to apply a charging voltage and a charging current to the battery cell wherein the adjustable voltage charging-profile having: a non-low-temperature charging stage for charging the battery cell using a charging profile adapted for battery cell temperatures above about zero degrees Celsius; and a low-temperature charging stage with a variable low-temperature stage charging current that decreases responsive to a battery cell temperature falling below zero degrees Celsius.

What is claimed as new and desired to be protected by Letters Patent of the United States is: 
     
       1. A charging system, comprising:
 a lithium ion energy storage element; 
 a charger; and 
 a battery management system that (i) determines when the lithium ion energy storage element has a temperature below 32 degrees Fahrenheit, and (ii) in response to the determination, applies a charging profile that sets a temperature-dependent current limit and a temperature-dependent voltage limit for the charger, wherein when the lithium ion energy storage element does not have the temperature below 32 degrees Fahrenheit, the battery management system applies a temperature-independent current limit, at least up to a maximum temperature, and a temperature-independent voltage limit. 
 
     
     
       2. The charging system of  claim 1 , wherein the maximum temperature is 104 degrees Fahrenheit. 
     
     
       3. The charging system of  claim 1 , wherein a DC model for the lithium ion energy storage element includes an imaginary R Bad  resistance in series with an R Nominal  resistance, wherein said R Bad  includes a function component responsive to one or more of said R Nominal , a state-of-charge (SOC) of the lithium ion energy storage element, and a temperature of the lithium ion energy storage element such that V cell  is about equal to a maximum battery cell voltage minus charging current times R Bad , wherein the circuit adjusts R Bad  over time using the function component so that a change in resistance of the battery cell is compensated for. 
     
     
       4. The charging system of  claim 3 , wherein said R Bad  includes a component that is about equal to a first constant k1 times R Nominal  minus a second constant k2 times SOC wherein said first constant k1 is about between 0 and 1 and wherein said second constant k2 is about 0.001/SOC %. 
     
     
       5. The charging system of  claim 4 , wherein said first constant k1 is about equal to 0.1. 
     
     
       6. The charging system of  claim 3 , wherein said R Nominal  is determined from a lookup table responsive to cell temperature, age, and SOC. 
     
     
       7. The charging system of  claim 3 , wherein said R Bad  is determined from a lookup table responsive to cell temperature, age, and SOC. 
     
     
       8. The charging system of  claim 3 , wherein said R Bad  is estimated in real-time or over time. 
     
     
       9. A charging method, comprising:
 determining when a lithium ion energy storage element in a charging system has a temperature below 32 degrees Fahrenheit; 
 in response to the determination, applying a charging profile that sets a temperature-dependent current limit and a temperature-dependent voltage limit for a charger of the charging system; and 
 when the lithium ion energy storage element does not have the temperature below 32 degrees Fahrenheit, applying a temperature-independent current limit, at least up to a maximum temperature, and a temperature-independent voltage limit. 
 
     
     
       10. The charging method of  claim 9 , wherein the maximum temperature is 104 degrees Fahrenheit. 
     
     
       11. The charging method of  claim 9 , wherein a DC model for the lithium ion energy storage element includes an imaginary R Bad  resistance in series with an R Nominal  resistance, wherein said R Bad  includes a function component responsive to one or more of said R Nominal , a state-of-charge (SOC) of the lithium ion energy storage element, and a temperature of the lithium ion energy storage element such that V cell  is about equal to a maximum battery cell voltage minus charging current times R Bad , wherein the circuit adjusts R Bad  over time using the function component so that a change in resistance of the battery cell is compensated for. 
     
     
       12. The charging method of  claim 11 , wherein said R Bad  includes a component that is about equal to a first constant k1 times R Nominal  minus a second constant k2 times SOC wherein said first constant k1 is about between 0 and 1 and wherein said second constant k2 is about 0.001/SOC %. 
     
     
       13. The charging method of  claim 12 , wherein said first constant k1 is about equal to 0.1. 
     
     
       14. The charging method of  claim 11 , wherein said R Nominal  is determined from a lookup table responsive to cell temperature, age, and SOC. 
     
     
       15. The charging method of  claim 11 , wherein said R Bad  is determined from a lookup table responsive to cell temperature, age, and SOC. 
     
     
       16. The charging method of  claim 11 , wherein said R Bad  is estimated in real-time or over time.